Imidazole-2-thiones are chemical compounds with relatively low toxicity [L. B. Bieqel, et al., Fundamental and Applied Toxicology, 27, 187-94, 1995] frequently used as substitutes for thioureas and have wide-spread applications such as chemical intermediates, catalysts for crosslinking adhesives [U.S. Pat. No. 5,296,586 Harper, 1999] and coatings [U.S. Pat. No. 5,162,482, Arduengo, 1992], activators for electroless plating [U.S. Pat. No. 5,554,211, Bokisa et al., 1996] and pharmaceuticals [U.S. Pat. No. 5,198,457, Yarrington, 1993].
These imidazol-2-thiones have been prepared by reacting vicinal diamines with compounds having a thiocarbonyl moiety and subsequently oxidizing the resulting reaction product [U.S. Pat. No. 7,115,748, Grast et al., 2006]; by reacting an imidazolium salt, sulfur and potassium carbonate in methanol solvent [B. Benac, et al., Organic Syntheses, vol. 64, pp. 92-95, 1986]; or by contacting an imidazolium salt with sulfur and sodium methoxide in an alcohol solvent [U.S. Pat. No. 5,104,993, Arduengo, 1992]. The afore mentioned conventional syntheses have various drawbacks including the use of solvents and, in some cases, multiple steps and/or protection/deprotection schemes. The alcohol solvent-based procedures suffer from the additional disadvantage that only a limited number of bases perform well in the reactions and the product imidazole-2-thione must be carefully purified to remove a malodorous reaction by-product.
The current invention provides a convenient solvent-free one-step route to a broad class of imidazole-2-thiones.